A ventilation insert of the type referred to at the outset is already known from the prior art. Ventilation inserts of this type typically have a layered construction in two or more plies.
EP 1 921 939 B1 shows a ventilation insert consisting of three plies. One of the plies forms a core element surrounded on both sides by two further functional plies in each case. The two functional plies are connected to each other by adhering or stitching together the two outer edges of the ventilation insert, so the swellable material sits loose and free between the functional plies. The disadvantage with this is that, on mechanically processing, in particular stitching, the ventilation insert, for example in textiles, the swellable material may egress at the needle insertion points because of the lack of fixing.
The core element comprises a swellable material or a vapor absorbent. A binder may bond the core material to either or both of the plies. There is a distinct increase in the basis weight of the ventilation insert on using a binder to fix the swellable material.
A core element disposed between the two functional plies without fixing by means of a binder is free to swell and able to take up a large amount of liquid. There is a distinct increase in the volume and the weight of the core element as a result. A limit is put on the basis weight by the two functional plies, which are spaced apart a certain homogeneous distance.
DE 10 2006 042 145 B3 discloses a ventilation insert consisting of seven plies. Three of the plies form a core element surrounded on both sides by two further functional plies in each case. The core element includes two air-pervious plies which enclose a swellable material. The further functional plies press the air-pervious plies of the core element together in sub-regions to create a chambered structure make up of regular chambers. This is done using functional plies made by injection molding, in which are disposed regularly shaped recesses. The manufacture of such an insert is costly and inconvenient. Not only are appreciable efforts needed to make the functional plies by injection molding, altogether seven plies have to be joined together to make one usable insert.
Owing to their multi-ply construction, the ventilation inserts in the above-described document have considerable size/thickness and also a high basis weight and are stiff and inflexible. This compromises the processing of the ventilation insert, in particular during stitching or adhering, in textiles.